The yeast plasmid 2 micron circle provides a simple experimental paradigm for the evolution of a selfish genome (or a benign molecular parasite). The genetic content and organization of this DNA molecule is devoted to maintaining itself stably in a population without unduly straining the metabolic machinery plasmid molecules at cell division. An amplification system, also encoded by the plasmid, adjusts plasmid copy number back to normal if and when it drops due to an occasional failure in partitioning. The amplification system must be exquisitely regulated for two reasons. First, it must be repressed under steady state growth, so that uncontrolled increase in copy number does not pose a threat to the host, and consequently to plasmid survival. Second, in the event of a fall in copy number, it must be commissioned immediately, so that copy number can be restored to the normal value within a short time. This project attempts to understand two aspects of the amplification mechanism. First, we wish to consider possible models for amplification, and test their predictions by using suitably designed plasmid substrates. Second we wish to analyze what biochemical steps mediated by the Flp recombinase, the central component of the amplification system, are important in the production of multiple plasmid copies from a single replication initiation event.